The invention relates to an anchor for anchoring in a drilled hole in concrete via a joining composition.
An anchor of this type is known comprising a threaded bolt having a threaded portion at one end, an expander cone widening toward its free end at the other end of the threaded bolt inserted in the drilled hole and an expandable sleeve enclosing the expander cone.
To anchor a threaded rod in concrete by a joining composition, a drilled hole is provided in the concrete which has an undercut in the vicinity of its bottom. German Patent Application DE-A1-35 16 866 describes this type of anchor. This known anchor is fixed by a method comprising inserting a glass capsule containing the joining composition into the drilled hole, the joining composition comprising polyester resin, a hardener and additives and crushing the glass capsule with the anchor. The joining composition is activated by mixing its components during and subsequently to the crushing with the anchor. Once the joining composition has hardened the anchor is fixedly bonded and anchored in the drilled hole. The anchorage is based in this instance essentially on the adhesive bond between the joining composition and the wall of the drilled hole. This bond is, however, substantially impaired if a crack is formed running through the anchoring point. By enlargement of the drilled hole as a result of the crack, the joining composition becomes detached from the wall of the drilled hole so that in the straight shank part of the anchor the retention forces are only slight. The known anchor nevertheless has a conical enlargement in the region of the undercut of the drilled hole so that comparatively large retention forces continue to exist there.
The construction of an anchor as a straight anchoring element presents problems because the joining composition becomes detached from the wall of the drilled hole when a crack occurs and thus the retention forces that continue to exist are only slight.